The invention is directed to golf balls, and more particularly to a ball having the optimal core compression, core diameter, cover hardness, and dimple configuration to provide superior playability capabilities with respect to softness and spin without sacrificing distance capabilities.
There are a number of physical properties that affect the performance of a golf ball. The core of the golf ball is the source of the ball""s energy. Among other things, the core affects the ball""s xe2x80x9cfeelxe2x80x9d and its initial velocity. The xe2x80x9cfeelxe2x80x9d is the overall sensation transmitted to the golfer through the golf ball after striking a ball. The initial velocity is the velocity at which the golf ball travels when first struck by the golf club. The initial velocity, together with the ball""s trajectory, determine how far a shot will travel.
Until the late 1960""s most golf balls were constructed as three-piece wound balls. In the three-piece wound ball, a solid or liquid-filled center is wound with rubber windings to form a core, which is then covered with a cover of compounds based on natural (balata or guta percha) or synthetic transpolyisoprene. During the manufacturing process, after the liquid-filled center is formed, it is frozen to make it as hard as possible so that it will retain its spherical shape while the rubber thread is wrapped around it.
These three-piece wound balls were known and are still known to provide acceptable flight distance and soft feel. Additionally, due to the relative softness of the balata cover, skilled golfers are able to impart various spins on the ball in order to control the ball""s flight path (e.g. xe2x80x9cfadexe2x80x9d or xe2x80x9cdrawxe2x80x9d) and check characteristics upon landing on a green.
With the advent of new materials developed through advances and experimentation in polymer chemistry, two-piece golf balls were developed. The primary difference between a two-piece golf ball and a three-piece golf ball is the elimination of the rubber thread windings found in the three-piece balls. A relatively large solid core in a two-piece ball takes the place of the relatively small center and thread windings of a three-piece ball core having the same overall diameter. With the elimination of the thread windings, there is no need to freeze the core during the manufacturing process of the two-piece golf ball.
Two-piece balls have proven to be more durable than three-piece balls when repeatedly struck with golf clubs and more durable when exposed to a variety of environmental conditions. An example of these environmental conditions is the high temperature commonly experienced in an automobile trunk. In addition, two piece balls are typically less expensive to manufacture than the three-piece wound balls. However, two-piece balls are, in general, considered to have inferior characteristics of feel and workability when compared to three-piece balls. Generally and historically, two piece balls use harder cover materials for increased durability. The xe2x80x9chardnessxe2x80x9d of a golf ball can affect the xe2x80x9cfeelxe2x80x9d of a ball and the sound or xe2x80x9cclickxe2x80x9d produced at contact. xe2x80x9cFeelxe2x80x9d is determined as the deformation (i.e. compression) of the ball under various load conditions applied across the ball""s diameter. Generally, the lower the compression value, the softer the xe2x80x9cfeel.xe2x80x9d Consequently, two-piece golf balls have a higher initial velocity. In addition, typically two-piece golf balls have more potential energy, which is derived primarily from the core. The cores in two piece golf balls are typically larger than the centers in three-piece golf balls.
In contrast, three-piece golf balls with their smaller centers historically use softer cover materials. These softer cover materials result in a lower initial velocity when compared to two-piece golf balls. However, this difference in the initial velocity may be somewhat made up by the windings in the three-piece golf ball.
In addition to manipulating the core and cover of a golf ball, for many years golf balls have been made with surface indentations or depressions, called dimples, to improve their aerodynamic properties in flight. Specifically, ball manufacturers have looked to dimple configurations in an effort to design a ball with superior distance capabilities. Many efforts have been made to select the optimum number, size and shape of dimples as well as their disposition around the outer surface of a generally spherically shaped golf ball.
Ball manufacturers are bound by regulations of the United States Golf Association (USGA) which control many characteristics of the ball, including the size and weight of the ball, the initial velocity of the ball when tested under specified conditions, the overall distance the ball travels when hit under specified test conditions, and the ball""s aerodynamic symmetry. Under USGA regulations, the diameter of the ball cannot be less than 1.680 inches, the weight of the ball cannot be greater than 1.620 ounces avoirdupois, the initial velocity of the ball cannot be greater than 250 feet per second when tested under specified conditions (with a maximum tolerance of +2%), the driver distance cannot exceed 280 yards when tested under specified conditions (with a test tolerance of +6%), and the ball must perform the same aerodynamically regardless of orientation.
While the USGA sets a limit for the distance a ball can travel under set test conditions, there is no upper limit on how far a player can hit a ball. For example, U.S. Pat. No. 4,142,727 to Shaw discloses the projection of a dodecahedron onto the ball as a basis for a dimple configuration in one of their preferred embodiments. The dodecahedron is formed by the projection of twelve (12) pentagons onto the balls surface. The preferred ball disclosed in this reference has a minimum of five (5) uninterrupted great circle paths present on the dimpled ball, and a major portion of the dimples present on the ball are within the boundaries of either a triangle, rhombus or pentagon.
In U.S. Pat. No. 5,192,078 to Woo discloses the use of a dodecahedron pattern in one of it preferred embodiments. The ball has six great circle paths which are free of dimples to further subdivide its surface pattern.
A problem with the prior art dimple configurations is that they fail to take into account other features of the ball, such as core size, core compression and cover hardness, which also influence how far a ball will travel.
U.S. Pat. No. 5,368,304 to Sullivan discloses a ball having a low spin rate, which in turn enables the ball to travel greater distances. According to the Sullivan patent, the low spin rate is the result of a soft core and hard cover. While the ""304 patent discloses the use of a soft core and hard cover to lower the spin rate, it does not disclose a dimple configuration for the ball.
The invention addresses the shortcomings of the aforementioned art through the use of a specific combination of cover material, dimple pattern and other novel features not found in any known art combination.
Accordingly, it is an object of the invention to provide a two-piece golf ball that has a soft feel in combination with superior distance capabilities.
It is another object of the invention to optimize the combination of core compression, core size, core composition, dimple configuration, cover composition, and cover hardness to provide a two-piece golf ball, which travels great distances, and at the same time complies with USGA regulations.
It is yet another object of the invention to provide a two-piece golf ball having a synthetic cover material that achieves excellent sound, feel, playability and flight performance qualities.
It is a further object of the invention to lower the cost of manufacturing a two-piece golf ball that has a soft feel in combination with superior distance capabilities.
It is still a further object of the invention is to provide a two-piece golf ball having superior distance, trajectory and flight stability.
Another object of the invention is to provide a two-piece golf ball having a surface divided into a plurality of polygonal configurations or shapes for the location of dimples for enhancing the aerodynamic properties of the golf ball.
The invention achieves the above-described objectives by providing a two piece golf ball having a solid rubber core, a synthetic ionomer resin cover, and a xe2x80x9cdodecahed-ronxe2x80x9d dimple pattern. The ball of the instant invention has a core compression in the range of 68 PGA to 82 PGA; a core diameter in the range of about 1.4 to 1.65 inches, preferably about 1.45 to about 1.6 inches, with a most preferred diameter of 1.504 inches to about 1.514 inches; a cover hardness in the range of about 60 to 70 Shore D and more preferably 62 Shore D to about 66 Shore D, and a dimple pattern based on the geometry of a dodecahedron.
This combination has been found to produce a ball with superior distance capabilities, which also satisfies USGA regulations. The use of these properties in the golf ball of the instant invention is based on the recognition that it is the combination of the core compression, core composition, core size, cover composition, cover hardness, dimple configuration, dimple size and dimple shape that will produce a ball that will travel the greatest distance without compromising shot-making feel.
The cover material must be constructed from a relatively stiff material, for example, synthetic thermoplastic materials. Most notably these synthetic thermoplastic materials are ionomeric resins. For superior properties and performance specific ionic polymer blends are required.
The present invention utilizes a greatly improved cover formulations for golf balls that corrects the deficiencies inherent in earlier blending attempts. It has been discovered that the blending of copolymers one or more of which may be an ionomer (such as ethylene-methacrylic acid, ethylene-acrylic copolymers or any other olefin-unsaturated carboxylic acid copolymer having similar properties wherein the acid level of the blend is 15-19% by total weight of the copolymer) having a moderately high modulus (45,000 to 60,000 PSI) with that of a moderately low modulus (10,000 to 14,000 PSI), wherein the acid groups of the ionic polymers are then partially neutralized by sodium, zinc, magnesium, or lithium either alone or in a any combination of the aforementioned ions results in a cover which has greater durability than prior art balls with a reduced hardness.
Therefore the playability of the ball is increased over prior art attempts at ionic polymer blends which attempted to blend very high modulus polymers with a very low modulus polymer producing a blend with a very high PDI, meaning a very broad range of individual polymer molecular weights within the blend which resulted in undesirable properties.
The cover material of the invention can be produced from the blends of various grades of resins formed from the co-polymerization of an olefin and an unsaturated carboxylic acid wherein at least one polymer is partially neutralized by a metal ion. A typical effective example of a copolymer of this invention is the copolymer of ethylene and unsaturated methacrylic acid. The invention is a blend of synthetic thermoplastic ionomeric resins produced by blending a moderately high modulus ionomeric (MHMI) polymer with a moderately low modulus polymer (MLMP). The average acid level of the final blend would be within the range of 13-19% by weight of acid. One or more of the copolymer blends of the instant invention are neutralized by a metal ion. The typical metal ions are lithium, magnesium, sodium or zinc. Examples of typical polymers that can be used in the cover composition which are commercially available and are sold by E. I. Dupont De Nemours and Company under the trademarks SURLYN and NUCREL.
As used herein, the term moderately high modulus ionomer (MHMI) shall be defined as a copolymer consisting of approximately 83-87% by weight of ethylene or other similarly performing olefin, 13-17% by weight of methacrylic acid or other similarly performing unsaturated carboxylic acid, where 10-90% of the acid groups are neutralized by sodium, zinc, magnesium or lithium ions. The MHMI will preferably have a melt index of 0.5 to 1.0 g/10 min., Shore D hardness of 60-70, and a flexural modulus between 45,000-55,000 PSI. The MHMI can have a melt index range of 0.5 to 7.0 g/10 min, Shore D hardness in a range of 55-75 and a flexural modulus from about 30,000 to 75,000 PSI.
As used herein, the term moderately low modulus polymer (MLMP) shall be defined as a copolymer consisting of approximately 79-83% by weight of ethylene or a similarly performing olefin, 13-17% by weight of methacrylic acid or similar performing unsaturated carboxylic acid. The MLMP will preferably have a melt index of 20-to 30-g/10 min., Shore D hardness of 57-67, and a flexural modulus between 10,000-14,000 PSI. An acceptable MLMP can have a melt index of 10 to 65 grams/10 min., Shore D hardness of 45 to 67, and a flexural modulus of about 5,000 to 25,000 PSI.
The methods for preparing the aforementioned polymers and ionomers are well known in the art and are described in U.S. Pat. No. 4,351,931 which is herein incorporated by reference. The method for preparation of high acid copolymers is a complicated process due to phase separation of the monomer-solvent phase. The method for producing a high acid copolymer is described in U.S. Pat. No. 4,351,931 that is also incorporated through reference herein. Once the ionic polymers have been produced the instant invention can be produced using any known conventional method of blending the copolymers.
A well know method in the art of blending polymers is through the use of a conventional extruder. The polymers can be melt blended in a temperature range of 175xc2x0 to 220xc2x0 C. and processed conventionally. The material is not excessively shear sensitive so any amount which results in sufficient mixing is acceptable. Once the cover material is sufficiently blended the golf ball can be produced by any known method. A conventional method of producing golf ball covers is described in U.S. Pat. No. 5,000,459 that is herein incorporated by reference.
Additionally compatible additives may be added to the cover blend of the instant invention. Examples of common additives are dyes and colorants such as titanium dioxide, zinc oxide, zinc sulfate and fluorescent pigments. As shown by U.S. Pat. No. 4,884,814 the loading of pigment or dye into a polymeric cover is dependant upon the base polymer utilized and the desired colorant to be added to the polymer. The final amount of colorant is dependent on the exact polymer blend and should be adjusted accordingly. The ideal loading level for colorant usually falls in the range of about 5% of the total weight of the cover.
Suitable for the present invention the cover blend composition will include 55-80% by weight of at least one MHMI polymers consisting of approximately 83-87% by weight of ethylene or a similarly performing olefin, 13-17% by weight of methacrylic acid or similar performing unsaturated carboxylic acid, where 10-90% of the acid groups are neutralized by sodium, zinc, magnesium or lithium ions and will have a melt index of preferably 0.5 to 1.0 g/10 min. but an acceptable range is 0.5 to 7.0 grams/10 min., preferably a Shore D hardness of 60-70 but an acceptable range is 55-75 Shore D, and preferably a flexural modulus between 45,000-55,000 PSI but an acceptable range is 30,000 to 75,000 PSI, and 20-45% by weight of at least one MLMP polymer consisting of approximately 79-83% by weight of ethylene or a similarly performing olefin, 17-21% by weight of methacrylic acid or similar performing unsaturated carboxylic acid and a preferable melt index of 20 to 30 g/10 min. but an acceptable range is 10 to 65 g/10 min., preferably having a Shore D hardness of 57-67 but an acceptable range is 45 to 67 Shore D, and a preferred flexural modulus between 10,000-14,000 PSI but an acceptable range is 5,000 to 25,000 PSI with the resulting final acid level between 13-21% by weight of acid. There are many commercial grades available which would satisfy these requirements of the instant invention.
In one preferred embodiment a blend of polymers with at least one polymer of a moderate modulus (10,000 to 14,000 PSI) and a high acid level having a Shore D of preferably approximately 63 but may range from 60 to 67, combined with at least one additional ionomeric copolymer having a high modulus (45,000 to 55,000 PSI), and medium acid level with a Shore D of approximately 65 but may range from 62 to 69 being partially neutralized by either sodium or zinc produces a cover with superior characteristics. This blend results in a golf ball cover with improved playability characteristics.
In another preferred embodiment the cover is a polymer blend of three copolymers with at least one of the polymers an ionic copolymers. The first component of the polymer blend consists of an ethylene/methacrylic acid copolymer with an acid level of 15% to 19% by weight wherein it is 20-45% by weight of the total blend, preferably 20 to 35%, and most preferably 25% by weight. The second component of the polymer blend consists of ethylene/methacrylic acid copolymer with an acid level of 15% neutralized by zinc ions wherein it is up to 50% by weight of the total blend, preferably 20 to 40%, and most preferably 30% by weight. The third component of the polymer blend consists of ethylene/methacrylic acid copolymer with an acid level of 15% neutralized by sodium ions wherein it is 10-90% by weight of the total blend, preferably 25 to 60%, and most preferably 45% by weight.
For the purposes of illustration the DUPONT ionomer resin grade designations for an ionomer define a low acid level is approximately 12% by weight, a medium acid level is approximately 15% by weight and a high acid level is approximately 19% by weight.
In a preferred embodiment composed of commercial available polymers from DUPONT for illustrative purposes only is the following; the polymer blend is 45% by weight of SURLYN 8920 or 8945, 30% by weight of SURLYN 9910 and 25% by weight of NUCREL 2906 or 925. As discussed previously, the cover material is comprised of ionomer resins and polymers available from E. I. du Pont de Nemours and Co. under the name SURLYN and NUCREL. The hardness of the cover produced by this blend formulation is about 64xc2x13 Shore D.
In the aforementioned illustrative cover formulation SURLYN 8920 can comprise from 10 to 90% by weight, SURLYN 9910 can comprise from 0 to 50% by weight and NUCREL can comprise 20 to 45% by weight of the total formulation. The invention is not limited to these commercial grades but other similar grades may be substituted.
As mentioned previously, in addition to manipulating the core and cover parameters in a golf ball, superior aerodynamic properties are also attributed to the dimple configuration on a golf ball. In the invention, the dimples are arranged on the surface of the golf ball based on the geometry of a dodecahedron. This configuration is achieved by dividing the outer spherical surface of a golf ball into a plurality of polygonal configurations using pentagons subdivided into triangular rows for locating a plurality of dimples on the outer surface of the golf ball. This first plurality of polygonal configurations is generally referred to herein as a xe2x80x9cmodified dodecahedronxe2x80x9d.
The first polygonal configurations consist of three pentagons symmetrically disposed around the first pole and three additional pentagons disposed around a second pole. Three pentagons in each polar region share a pole as a common vertex for a total of six pentagons associated with the polar regions. There are six remaining pentagons which are associated with the equatorial region (mold parting line) of the ball surface. The outer surface has a plurality of dimples of different sizes. For this embodiment, the dimples are of first, second and third sizes and are generally located to have a pattern associated with the pentagons and subsequent triangles and rows. The dodecahedron pattern is further defined by the presence of ten great circles paths upon the ball, one of which is the equator or parting line of the ball. Dimples are preferably circular in shape, but can have a non-circular shape within the scope of this invention.
The combination of the aforementioned core, cover and dimple specifications produces a golf ball that possesses noticeable improvements in playability (i.e. spin properties) without sacrificing the ball""s durability (i.e. impact resistance etc.) which in turn relates directly to the distance a ball will travel when struck. In addition, the instant invention provides a golf ball composition that exhibits the desired properties of the three-piece wound ball (e.g. long distance in combination with a soft feel), but with the lower manufacture cost associated with the two-piece ball. These and other objects of the instant invention will be apparent from a reading of the following detailed description of the instant invention.